feat(frontend): rebuild as SSR with server-authoritative shared state

Rombak total alur data frontend: dari static-export CSR (tiap browser
fetch sendiri + akumulasi state voice per-tab) jadi server-side rendering.

Frontend (Next.js):
- next.config: output export -> standalone; halaman jadi server components
- server data layer baru src/lib/api/server.ts (GMW_BACKEND_URL, no window)
- dashboard/media/messages/moderation/recordings/voice page -> RSC yang
  fetch backend di render-time, seed ke client view (SWR fallbackData)
- hook-hook utama terima initialData -> first paint data server, revalidate
  SWR setelahnya, tanpa spinner-blank-load
- messages: guild/channel/tab/selected dibaca dari URL di server, page awal
  di-fetch server-side

Shared realtime state (voice) server-authoritative:
- backend src/modules/voice/live-speaker.ts: agregat voice_active_user dari
  gateway jadi snapshot authoritatif (single source of truth semua browser)
- GET /api/voice/status kini include activeSpeakers
- WS initial states kirim voice_state snapshot saat connect (late join
  langsung dapat state yang sama, bukan daftar kosong)
- useSpeakers seed dari server snapshot + voice_state full-replace +
  voice_active_user delta upsert

Deploy:
- flake.nix: frontend package build SSR standalone (server.js wrapper,
  GMW_FRONTEND_PORT=4017); proxy nginx template proxy / -> Next server,
  /api + /ws tetap ke backend :4001

services/backend/src/ws/server.ts

@@ -66,6 +66,22 @@ async function sendInitialStates(ws: WebSocket): Promise<void> {
   } catch (err) {
     logger.warn({ err }, "Failed to send initial media_state");
   }
+
+  // Send initial live-voice snapshot (shared authoritative state — a browser
+  // joining mid-call sees the same speakers as everyone else, not an empty DB).
+  try {
+    const { getActiveSpeakers } = await import(
+      "../modules/voice/live-speaker.js"
+    );
+    ws.send(
+      JSON.stringify({
+        type: "voice_state",
+        state: { activeSpeakers: getActiveSpeakers() },
+      }),
+    );
+  } catch (err) {
+    logger.warn({ err }, "Failed to send initial voice_state");
+  }
 }
 
 export function closeWebSocketServer(): void {